Presently, hard disk drives (abbreviated below as HDD) have become the mainstream of external storage devices of computers. An HDD uses a magnetic recording medium having a magnetic film as a recording material, and an alignment servo signal of a writing/reading head prerecorded on the magnetic recording medium using a magnetic transfer technique.
In an HDD, the recording and playback of data is transferred (read/written) while the magnetic head is levitated closely (about several tens of nm) above the rotating recording medium, by a levitation mechanism called a slider. Bit information on the magnetic recording medium is stored in concentrically disposed data tracks, and a data recording/playback head is moved and positioned at a high speed to the target data track on the medium surface to record and play back data.
Alignment signals (servo signals) for detecting the relative position between the head and the data tracks are concentrically written on the magnetic recording medium surface, and the head conducting the recording and playback of data detects its own position at fixed time intervals. After the magnetic recording medium has been loaded into an HDD device, writing signals are written thereto using a dedicated device called a servo writer so that the centers of the writing signals of the servo signals do not become decentered from the center of the medium (or center of locus of the head). At present, recording density has reached 100 Gbits/in2 at the development stage, and recording capacity is increasing at an annual rate of 60%. In accompaniment therewith, the density of servo signals for the head to detect its own position is also rising, and the trend is such that the writing time of the servo signals is also increasing annually. This increase in the writing time of the servo signals is largely the cause of the drop in the productivity and an increase in the cost of HDDs.
Recently, with respect to a method where the servo signals are written using the signal writing head of the servo writer, remarkable technological developments have been made that attempt to shorten the writing time of servo information by writing the entire servo signals at once by magnetic transfer technology. FIGS. 12A–12C and 13A–13B illustrate this magnetic transfer technology (see JP-A-2001-34939 for example). FIG. 13A illustrates a state where a permanent magnet 2 is moved over the surface of a magnetic recording medium 1, while maintaining a fixed interval (1 mm or less), represented from a cross-sectional direction of a substrate. A magnetic film 4 formed on a substrate 3 is initially not in a state where it has been unidirectionally magnetized, but is unidirectionally magnetized by a magnetic field leaking from a gap in the permanent magnet 2 (arrows 5 written in the magnetic film in the drawing represent the direction of magnetization). This process is called an initial demagnetization process. An arrow 6 in FIG. 12A represents the movement path of the permanent magnet on the magnetic recording medium, and the magnetic layer is uniformly magnetized in the circumferential direction.
FIG. 12B illustrates a state where a master disk 7 for magnetic transfer (abbreviated below as a master disk) is disposed and positioned above the magnetic recording medium 1. FIG. 12C illustrates a state where magnetic transfer is conducted by tightly adhering the master disk to the surface of the magnetic recording medium and moving the permanent magnet for magnetic transfer along the movement path in the drawing (represented by arrow 6).
FIG. 13B illustrates the magnetic transfer technique. The master disk 7 has soft magnetic films 9 (e.g., Co soft magnetic films) imbedded in the surface of a silicon substrate 8 that contacts the medium surface. When the substrate 8 with the pattern of the embedded soft magnetic films is interposed between the permanent magnet 2 and the magnetic recording medium 1, the magnetic field (the orientation of the transfer signal writing magnetic field is in the direction opposite to that of the demagnetization magnetic field) that has leaked from the permanent magnet 2 and penetrated the silicon substrate 8 is again transmitted through the silicon substrate 8 at positions where there is no soft magnetic film so that the magnetic layer can be magnetized (the direction of magnetization thereof is represented by arrows 10), but passes through the soft magnetic films 9 at the portions where the soft magnetic pattern is present to form magnetic paths of small magnetic resistance. For this reason, the magnetic field leaking from the silicon substrate 8 at the positions where the soft magnetic layers are present becomes small and new magnetization writing is not made. Magnetic transfer of the servo signals is thus conducted by the above technique. It should be noted that a technology that conducts center alignment of the master disk for magnetic transfer and the magnetic recording medium has also been proposed (see JP-A-11-175973 for example).
Also, using both sides of the magnetic recording medium of the HDD by forming magnetic films on the surface and undersurface to increase the recording capacity per single medium has become the mainstream. Of the magnetic patterns recorded on the magnetic recording medium, there are the above-described servo pattern and a data pattern. For this reason, magnetic transfer is being conducted by tightly adhering a master disk to both surface sides of the magnetic recording medium (see JP-A-2000-67433 for example). A transparent base material can also be used as a master disk (see JP-A-2000-197647 for example).
In an HDD device using a magnetic recording medium where magnetic films are formed on the surface and undersurface, numerous magnetic disks are disposed, magnetic heads are individually disposed at the surface and undersurface thereof. Moreover, only an HSA (Head Stack Assembly) disposed with a head corresponding to a cylinder having a designated data region is controlled by servo control to be at a predetermined position, while not controlling the other HSA. Thus, when the misalignment between the surface and undersurface servo patterns is large in a case where the reading and writing cylinder is changed from the surface to the undersurface, there is the problem that time is required until stabilization of the position by the servo of the HSA at the undersurface and, as a result, settling time corresponding to the reading time of the data after the cylinder switching increases. For this reason, it becomes extremely important for there to be no misalignment between the surface and undersurface magnetic patterns of the magnetic recording medium to not compromise high-speed data access of the HDD. With respect to conventional magnetic transfer target patterns, because photoprocessing technology that forms the master disks has been based on a μm rule, there have only been servo patterns having a large pattern width. But when consideration is given to the fact that the utility of magnetic transfer and photoprocessing technology are progressing and have become based on a sub-μm rule, data patterns should also be thought of as transfer targets in addition to the conventional servo patterns and magnetic transfer by high-density master disks to the magnetic recording medium becoming necessary.
Thus, there is a need to precisely align the magnetic pattern of a surface-use master disk and the magnetic pattern of an undersurface-use master disk of a magnetic recording medium, and to precisely align the center of the magnetic recording medium with the centers of the magnetic patterns of the master disks while the surface and undersurface master disks are precisely aligned. The present invention addresses this need.